(1) Field of the Invention
This invention relates to a method of and an apparatus for displaying the output, i.e., the torque or horsepower of an internal combustion engine while the engine is operating.
(2) Description of the Related Art
The speed, cooling water temperature, etc., of an internal combustion engine for a vehicle are usually displayed on indicators on the dashboard. The output torque of the engine, however, is not usually displayed or used for various control mechanisms such as an automatic transmission of the vehicle. The reason for this is because the torque is barely detectable while the vehicle is running.
To accurately measure the torque of the internal combustion engine of the vehicle, it is necessary to carry out, for example, a bench test using a chassis dynamo. Alternatively, a torque sensor can be used to detect a small torsion on a shaft disposed in a power transmission system.
The former requires large facilities that are naturally not applicable to a vehicle that is moving. The latter is also not practical because the torque sensor is very expensive and not durable.
This applicant has proposed an apparatus for indirectly detecting the torque of an internal combustion engine, according to information in Japanese Unexamined Utility Model Publication No. 3-42041. This apparatus detects, in a vehicle engine, an intake air quantity per revolution (Q/N) according to an intake air flow quantity (Q) and a rotation speed (N) of the engine, multiplies the value (Q/N) by a predetermined constant, subtracts a loss corresponding value from the multiplication result, and then provides the output torque of the engine, when the engine is operating.
This apparatus, however, calculates the output torque and horsepower of the engine only from the intake air flow quantity and rotation speed of the engine with no attention to a change in air-fuel ratio (a mixture ratio) due to a fluctuation in the flow quantity of fuel supplied to the engine. This may cause the displayed torque and horsepower measurements to deviate. The measuring capability of this apparatus, therefore, is not sufficient.
Such deviation particularly occurs in a high-speed heavy-load operation region of the engine. It is necessary to improve the detection accuracy of the apparatus, particulary in this region. The apparatus also makes an erroneous detection when the engine is unsound causing a fluctuation in the fuel flow quantity and air-fuel ratio even when the engine is operating under constant conditions. The apparatus may cause a large measurement error in, for example, a turbo charged vehicle whose air-fuel ratio drastically changes when the accelerator is fully opened.
The displayed torque and horsepower measurements of the apparatus may also deviate from the actual measurements when an ignition timing of the engine fluctuates widely.